A geographic information services (GIS) data collection device includes a global positioning system and/or global navigational satellite system (GPS/GNSS) receiver, a laser rangefinder, pitch and roll sensors, a digital compass, a video camera, a mobile processor and a display. Such GIS devices are often used for collecting or confirming the position and dimensions of trees, manhole covers, power lines, power poles, building structures, streams, ponds, lakes, hydrants, fence lines, park benches, etc.
In operation, GPS/GNSS measurements provide the location of the GIS device itself while laser rangefinder and pitch and roll measurements provide the location of a target object with respect to the GIS device. State-of-the-art, commercially available GIS devices may have GPS/GNSS accuracy of approximately 10-100 cm, compass heading accuracy of approximately 1-2 degrees and laser rangefinder accuracy of approximately 5 cm. Accuracy is worse for distant targets compared to near ones because of the increasing effect of compass heading error.
An interesting example of GIS data collection was a project to map helicopter landing zones in thousands of square miles of rural area in the Ozark Mountains in Arkansas. A landing zone is an unobstructed area of at least 100×100 feet, and flat enough to land a helicopter safely. The project involved confirming the location of existing landing zones and mapping new ones. Workers were surprised to learn that the coordinates of many existing landing zones were wildly inaccurate. One was in the middle of a lake.
Landing zone coordinates may be defined by mapping the locations of obstacles, such as trees, power poles, large rocks, etc., at the periphery. In projects like this, rather than taking GPS/GNSS measurements under tree canopy and perhaps suffering degraded accuracy, workers can instead remain in an open area and aim a GIS device's laser rangefinder at targets to collect their locations. In Arkansas, once verified landing zone coordinates were entered into a database, response times for emergency workers traveling by helicopter were dramatically reduced, and medical emergencies, such as heart attacks, were less likely to be fatal.
Rangefinders of conventional GIS devices show an image of the object being measured. Even so, it is not always clear to a user what the device is measuring. When target objects are close together, the wrong one may be measured. If GPS/GNSS signals are weak at the position of the GIS device, accuracy may not be as good as expected. Mistakes and problems like these reduce the value of GIS data. Thus, there exists a need to make mobile GIS data collection devices even more useful by helping users understand measurements quickly and intuitively.